This invention relates to an air-pressure vibration damping apparatus, and an exposure apparatus and a device manufacturing method using the vibration damping apparatus. The vibration damping apparatus is placed on a mounting floor, supporting an upper apparatus such as an exposure apparatus by using air springs, damps vibration from the mounting floor to the upper apparatus, and suppresses vibration of the upper apparatus, by controlling the inner air pressures of the air springs. The air springs generally function as actuators for positioning the absolute or relative position of the upper apparatus with respect to the setting surface.
In recent years, semiconductor devices are manufactured by using a so-called "stepper" exposure apparatus. That is, the device is sequentially positioned at a desired position on a sensitized substrate (a wafer or a glass substrate on which a photoresist layer is provided) on which a reticle pattern image is projected via a projection optical system. The sensitized substrate is held on X- and Y-stages, and the positioned device is exposed there. Especially, in this manufacturing method, high-density semiconductors are made. Therefore, it is necessary to transfer a finer pattern on the exposure substrate.
In this situation, the level of a vibration damping technique for the exposure apparatus must be increased, and various vibration damping apparatuses are known for the purpose of preventing vibration from the mounting floor to the exposure apparatus.
Conventionally, a passive vibration-damping apparatus using mechanical springs and dash pots is widely employed. This apparatus damps vibration from a mounting floor by reducing the spring constant to lower the resonance frequency of the vibration system, and widening the vibration-damping area, thus suppressing vibration transmittance to a low level. Further, with respect to vibration which occurs on an exposure apparatus caused by step motions of the X- and Y- stages and the like, the apparatus absorbs vibration energy by increasing the damping rate of the dash pots, thus suppressing vibration quickly.
Recently, as the vibration damping apparatus, an active or semiactive vibration-damping apparatus which actively controls an object apparatus, is becoming popular. The active vibration-damping apparatus has sensors for detecting vibration of the object apparatus, e.g., an exposure apparatus, and the relative position of the exposure apparatus with respect to a mounting floor. Based on detection signals from the sensors, energy from actuators of the vibration damping apparatus is applied to the exposure apparatus, to positively enhance damping of vibration from the mounting floor to the exposure apparatus and vibration which occurs on the exposure apparatus by step motions of the X- and Y- stages.
The actuators used in the active vibration-damping apparatus are briefly divided into electric actuators and air actuators. Air-pressure active vibration-damping apparatuses have three or more air springs for supporting an exposure apparatus in the vertical direction. The respective air springs have inner air pressures at an equilibrium. The air springs generate counter forces to support the exposure apparatus. On the exposure apparatus, the step motions of the X- and Y- stages are regularly made upon each exposure. The moving load tilts the exposure apparatus, which changes the relative position of the exposure apparatus with respect to the mounting floor. The posture of the exposure apparatus is detected by sensors, mounted on the active vibration-damping apparatus, for monitoring the relative position of the exposure apparatus with respect to the mounting floor. In accordance with detection signals from the sensor, servo valves, electromagnetic valves and the like, as electricity/air-pressure converters are opened/closed by a controller, to provide/release air to/from the respective air springs, thus control the inner air pressures of the air springs. The exposure apparatus is returned by the air springs to restore the initial relative position with respect to the mounting floor with high precision. At the same time, based on detection signals from sensors monitoring vibration of the exposure apparatus, the electricity/air-pressure converters are opened/closed to change the inner air pressures of the air springs, to generate position-corrected forces to the springs to damp vibration. This damps resonance vibration of a vibration system of the exposure apparatus, and obtains a high vibration-damping effect. As a result, the exposure apparatus can be isolated from vibration of the mounting floor, and the vibration of the exposure apparatus can be quickly suppressed.
A semiconductor device is manufactured by overlaying a number of layers of circuit patterns on a sensitized substrate. In the exposure apparatus, to transfer a second or subsequent circuit pattern on the sensitized substrate, relative positioning (alignment) between the prior circuit pattern formed on the sensitized substrate and a reticle to be projected is required. The conventional active vibration-damping apparatus has been effective by virtue of its vibration damping of the exposure apparatus, however, it has the following problems for high precision alignment corresponding to high-density semiconductor devices.
In the conventional active vibration-damping apparatus, at each step motion of the X- and Y- stages, the inner air pressures of the plural air springs are controlled so as to maintain the posture of the exposure apparatus where the center of gravity has changed. Accordingly, the balance of the supporting counter forces generated by the respective air springs changes at each step motion, which deforms the exposure apparatus in a nano-order. This deformation affects the positioning of the reticle pattern and sensitized substrate, and disturbs the relative position among aligning units such as the projection optical system, an alignment scope and the like, mounted on the exposure apparatus.
To manufacture high-density semiconductor devices, the change of supporting counter forces of the air springs due to the step motions of the X- and Y- stages must be suppressed to a low level, and the supporting counter forces must be obtained in accordance with the positions of the X- and Y- stages. This reduces the change of relative positions of the aligning units mounted on the exposure apparatus, and upon transferring a second or subsequent layer of a circuit pattern, restores the relative positions when the prior layer of the circuit pattern has been transferred. As a result, aligning ability can be improved.
However, in a case when the conventional active vibration-damping apparatus has four or more air springs, it is very difficult to restore the supporting counter forces in accordance with the position of the X- and Y- stages. Since a plane is defined by three points, four or more supporting point(s) causes an unstable support which disturbs the plane. Accordingly, if a number of layers of circuit patterns are overlaid, the equilibrium of the inner air pressures of the four or more air springs when exposing the first layer cannot be restored exactly to for exposure of the second layer. In this case, the equilibrium of the inner pressure the air springs changes by a large amount, and the inner pressures greatly change. This degrades the aligning performance of the vibration damping apparatus.
On the other hand, in a case when the active vibration-damping apparatus has three air springs, the equilibrium of the inner air pressures of the respective air springs, determined upon step motions of the X- and Y- stages on the exposure apparatus, can be fixed depending upon the position of the stepped X- and Y- stages. However, the number of supporting points for the exposure apparatus is limited to three, and this narrows the freedom of designing the vibration damping apparatus.